1. Field of the Invention
This invention relates to an acoustic signal processing apparatus. More particularly, it relates to an acoustic signal processing apparatus in which pre-set acoustic characteristics are added to input voice signals.
2. Description of the Related Art
The present Assignee has proposed in Japanese patent Application No.6-176775 (Japanese Patent lying-Open No.8-44389) entitled `Acoustic Signal Processing Apparatus` an acoustic signal processing apparatus in which the input voice and the voice having an interval spaced by a pre-set pitch from the interval of the input voice are synthesized to give an acoustic effect (unison effect) in which plural singers are singing despite the fact that only one person is singing. The `unison` herein means singing or music performance in unison.
FIG. 1 shows, in a block diagram, an acoustic signal processing apparatus 101 for according the unison effect as proposed in Japanese Laying Open Patent No.8-4389. The acoustic signal processing apparatus 101 includes a microphone amplifier 102 for amplifying an input signal from a microphone (M-IN), such as voice of a performer entered via a microphone, not shown, and an A/D converter 103 for converting acoustic signals amplified by the microphone amplifier 102 into digital acoustic signals. The acoustic signal processing apparatus 101 also includes a unison voice generator 104 and a line amplifier 105 for amplifying an input signal (L-IN), such as musical performance signals, as accompaniment, reproduced by a compact disc reproducing device or a video disc reproducing device. The acoustic signal processing apparatus 101 also includes an A/D converter 106 for converting the music performance signals, amplified by the line amplifier 105, into digital music signals, a key control circuit 107, a music vocal mixing unit 108 and a D/A converter 109.
The unison voice generator 104 includes an interval converting circuit 110 and a synthesizing circuit 111. The interval converting circuit 110 converts the interval of the digital signal into signals of an interval spaced apart a pre-set pitch from the interval of the input acoustic signal. The synthesis circuit 111 synthesizes the digital signal and an output digital signal of the interval converting circuit 110 by digital signal processing.
The result is that the acoustic signal processing apparatus 101 synthesizes the singing voice of a vocal performer with the singing voice of an interval different from the interval of the singing voice of the performer, even if only one vocal performer is singing, thus giving the unison effect, that is the effect as if plural vocal performers are singing. The acoustic signal processing apparatus 101 may also be configured so that it has plural interval conversion circuits 110 for generating plural different singing voices of different intervals and synthesizing the different singing voices. With the acoustic signal processing apparatus 101, the user can optionally select whether or not the unison effect is used, or set the pitch for interval conversion.
The key control circuit 107 can convert the interval of the music performance signals from, for example, a compact disc reproducing apparatus, based on an interval specifying signal as set by the user, to output the converted music performance signals.
The music vocal mixing unit 108 includes an equalizer 112 for generating, by digital signal processing, a digital signal converted in frequency characteristics based on an output digital signal from the unison voice generating unit 104, and a synthesis circuit 113 for synthesizing the digital signal outputted by the unison voice generating unit 104 and the digital signal outputted by the equalizer 112. The music vocal mixing unit 108 also includes an echo processing circuit 114 for generating an echo by digital signal processing based on the output digital signals of the synthesis circuit 113 and a synthesis circuit 115 for synthesizing, by digital signal processing, the output digital signal of the synthesis circuit 113 and digital signals equivalent to an echo outputted by the echo processing circuit 114. The music vocal mixing unit 108 also includes an equalizer 116 for converting, by digital signal processing, the frequency characteristics of the digital signal as accompaniment outputted by the key control circuit 107 and a synthesis circuit 117 for synthesizing the output digital signal of the synthesis circuit 115 and the output digital signal of the equalizer 116.
The equalizers 112, 116 can set the frequency characteristics desired by the user. The frequency characteristics of the equalizers 112, 116 can be adjusted separately or together. The echo time of the echo sound generated by the echo processing circuit 114 can be optionally set by the user.
The output digital signals of the synthesis circuit 117, synthesized from the vocal and the music, are converted by the D/A converter 109 into analog vocal/music signals so as to be outputted as acoustic output signal (A-OUT).
In the above-described acoustic signal processing apparatus 101, the input signal from a microphone is converted by the A/D converter 103 into digital signals, which are then processed by digital signal processing for according the vocal having the interval different from that of the vocal entered via the microphone, converting the frequency or according the echo. Since the acoustic signal processing apparatus 101 performs the signal processing as digital signal processing, high-precision digital processing operations are required, thus requiring high-performance A/D converter 103 or D/A converter 109 with a larger number of bits and with a higher sampling frequency.
The acoustic quality of the acoustic signal processing apparatus depends to a large extent on the performance of the A/D converter or the D/A converter in use, such that, if inexpensive A/D converter or D/A converter with low signal processing accuracy is used, sufficient acoustic quality cannot be assured. It is therefore necessary to use an A/D converter 103 or a D/A converter 109 that are high in signal processing accuracy and therefore are rather expensive.
In the acoustic signal processing apparatus 101, if the unison effect, modification of the frequency characteristics by the equalizer or the echo effect is not used but simply the voice as collected by the microphone and the accompaniment are synthesized to produce the acoustic output signal (A-OUT), the number of quantization bits needs to be increased for securing a sufficient dynamic range for faithfully processing the voice by digital signal processing. In addition, the sampling frequency needs to be high for securing the sufficient acoustic signal quality. The result is that the acoustic signal processing apparatus 101 is complex in hardware structure and expensive A/D and D/A converters need to be used, thus raising the cost.
In the acoustic signal processing apparatus 101, pre-set delay is produced due to digital signal processing of the input microphone signal. In addition, in digital signal processing, the quantization noise is unavoidably produced in digital signal processing. Thus, if the acoustic signal processing apparatus is applied to a karaoke system in which the input via the microphone is outputted on a real-time basis, a phase difference or time shift is generated between the microphone input and the signal processed by digital signal processing, or the signal-to-noise (SN) ratio is lowered. Because of this a desired high acoustic effect cannot be achieved.